https://www.cnet.com/news/avengers-endgame-physics-problem-spoilers/

"Very simply stated, I don't believe that anything that we have learned about gravity and quantum mechanics suggests that time travel to the past is possible," said Leonard Susskind, an influential Stanford professor whose claim to physics fame is helping to create string theory, a fundamental rethink of the universe's laws.

Even the most plausible approach to time travel -- wormholes that could link different points in the universe's fabric of time and space -- requires some seriously weird and potentially nonexistent forms of matter. You're not going to be able to travel back in time to murder your grandfather, much less resurrect the Marvel Cinematic Universe's Spider-Man franchise.